The invention relates to a guide member for a linear-movement guide, arranged on and executing movements in longitudinal direction along a rail, which guide member comprises at least one roll body circuit, wherein each roll body circuit has a return channel, a bearing zone, as well as two deflection channels that connect the return channel and the bearing zone, which further comprises several roll bodies in each roll body circuit and is provided with guide means for guiding the roll bodies inside the roll body circuit.
Linear guides for roller bearings are used in many areas of technology, in which one structural component is to be moved in a straight line and without frictional losses, if possible, relative to another structural component. Machine tools represent one example for this. A carriage or slide serves as guide member for such guides and is guided along a rail over roll bodies such as balls, rollers or needles. The roll bodies in that case circulate in closed roll body circuits of the carriage. Normally they have a bearing zone, in which the roll bodies fit flush against a bearing surface of the carriage and against the rail, thereby supporting the load to be moved. Owing to the linear movement of the carriage, the roll bodies move from the bearing zone into a first deflection channel, in which the roll bodies are transferred from the bearing zone to the return channel. Following passage through the return channel, the roll bodies travel via a second deflection channel back to the bearing zone.
Using plastic components for the carriage surfaces, which come in contact with the roll bodies, has long been known as a way to minimize wear on the roll bodies and improving the quietness of running of a linear guide. German Patent 35 40 099, for example, discloses providing the guide surfaces of the return channel as separately produced sleeves, which are inserted later on into corresponding recesses in the metal base body of the carriage. With this type of design, it can be considered a disadvantage that an accurate production and extremely exact and involved assembly are required. Additional transition points also develop on this two-part sleeve design, which can reduce the quietness of running.
German Patent 43 31 014 C2 furthermore describes producing guide means in the bearing zones and the return channels by spraying the plastic guide surfaces directly onto the metal base body of the carriage with the aid of an injection-molding technique. However, this known carriage also requires a relatively involved lubricant supply, as does the previously mentioned carriage. For the lubricant supply, lubricant is fed from the outside to the inside of the carriage in order to lubricate the roll bodies normally made of metal. This is designed to reduce wear on the roll bodies and thus extend the service life of the guide. The known lubricant-supply methods, however, increase the design expenditure and thus make the linear guide more expensive. Also, it is not possible to rule out a defect in the lubricant supply, which can lead to considerable damage to the machine in which the linear guide is used.
Thus, it is the object of the invention to create a carriage with which the above-described disadvantages in prior art can be avoided. In particular, the goal is to create a carriage, which makes it possible, at least for the most part, to dispense with a lubricant supply or lubricant feeding of the known type.
With a guide member of the aforementioned type, this object is solved in that at least a portion of the material for forming the guide means contains or is bonded to a material, which reduces the wear on the linear guide, particularly the wear on the roll bodies. Guides according to the invention thus can contain a multi-component material, to which the wear-reducing material is bonded similar to a matrix. The resulting material is heterogeneous and, with respect to its structure, can be compared to standard composites. In contrast to these standard composites, a component of the xe2x80x9ccompositesxe2x80x9d according to the invention is designed to reduce friction with the roll bodies and does not function, at least not primarily, to increase the material strength.
It has turned out that this material can be processed particularly well if it contains a thermoplastic plastic with an added solid lubricant, which must be processed with an injection-molding technique. The guide member can be produced with very little expenditure if complete components of the guide member are fashioned from the one material only and with the injection-molding technique. The solid lubricant in this case can be formulated in different ways. However, it has proven advantageous if the solid lubricant is added in the form of fibers. With this preferred embodiment, the fibers should permit the dry run, meaning the circulation without lubricant, of the roll bodies.
In practical tests, using fibers made of PTFE (poly tetrafluoroethylene), so-called Teflon(copyright) (commercially used mark and registered trademark of the DuPont Company) has proven advantageous because it leads to particularly low wear of the roll bodies. To be sure, Teflon is known to be particularly susceptible to wear at high surface pressure and the wear-resistance required in roller bearings for linear guides is particularly high. Nevertheless, it has turned out surprisingly that comparably high service life times for linear-movement guides can be reached if PTFE particles are added to a thermoplastic plastic suitable for the injection-molding technique, e.g. POM plastics belonging to the group of poly acetals (poly oxymethylene). Alternative to PTFE, poly fluoroethylene propylene or perfluoroalkoxy can also be used.
Furthermore, it has proven advantageous if the particles are present in the form of fibers, having a length between 100 xcexcm and 700 xcexcm, preferably between 170 xcexcm and 500 xcexcm and having a width between 10 xcexcm and 100 xcexcm, preferably between 20 xcexcm and 40 xcexcm. At least in the surface region of the guide means, the particles should account for a volume share of 5% to 35%, preferably 12% to 15%, measured on the total material volume. Of course, the particles can also be present in formulations other than fibers and in dimensions and amounts other than those mentioned in the above. For example, the particles can also be present in the form of balls.
With respect to the service life of linear guides, particularly lubricant-free linear guides, especially good results can be achieved if a ceramic material is used for at least some of the roll bodies, e.g. Si3N4, ZrO2 or Al2O3. In this connection, the applicant has filed in 1998 the Swiss Patent Application 1388/98. A particularly favorable combination is given with the use of such roll bodies, together with the previously mentioned use of fibers or particles made of PTFE in a plastic for the guide means.
Of course, it is also possible to use materials other than PTFE, which are added to the material for the guide means. For this, all dry lubricants can be used in principle, e.g. sulfide-bonding halides or perfluorinated plastics. Particularly suitable are materials that result in the highest possible reduction in the frictional coefficient between roll bodies and the respective guide means with the lowest possible abrasive wear of the solid particles. MoS2 is also a suitable material for this, in addition to PTFE.
Finally, the wear-reducing materials can also be present in the form of a coating that is deposited on a guide means. In that case, the wear-reducing materials are present only at the guide surfaces or running surfaces of the guide means or the rail or are additionally deposited on the previously described guide means. A coating of this type can be applied, for example, by spraying it on with one or several nozzles, by submerging the guide means or the rail in a bath, or by using galvanic processes. Coatings of this type can contain, for example, poly tetrafluoroethylene, poly tetrafluoroethylene propylene, perfluoroalkoxy, diamond-like amorphous carbon, chromium and/or MoS2.
Basically it is not necessary for all guide means of a roll body circuit to be provided with a material according to the invention. It has turned out to be sufficient if at least some of the guide means are provided with it. Thus, it makes sense if at least the guide means of the deflection channels are designed in this way, which already results in the advantage of the friction being reduced at the locations with the highest load. In addition, a solution that is favorable with respect to production technology can be achieved.
Additional preferred embodiments of the invention result from the dependent claims.